Bottom Line:
Amoeba-associated microorganisms (AAMs) are frequently isolated from hospital water networks and are reported to be associated to cases of community and hospital-acquired pneumonia.Our results show that some AAMs may be more frequently detected in patients who had hospital-acquired pneumonia than in controls, whereas other AAMs are ubiquitously detected.Our work partially confirms the results of previous studies, which show that ICU patients would be exposed to water amoeba-associated microorganisms, and provides information about the magnitude of AAM infection in ICU patients, especially patients that have a prolonged ICU stay.

Background: Patients admitted to intensive care units are frequently exposed to pathogenic microorganisms present in their environment. Exposure to these microbes may lead to the development of hospital-acquired infections that complicate the illness and may be fatal. Amoeba-associated microorganisms (AAMs) are frequently isolated from hospital water networks and are reported to be associated to cases of community and hospital-acquired pneumonia.

Methodology/principal findings: We used a multiplexed immunofluorescence assay to test for the presence of antibodies against AAMs in sera of intensive care unit (ICU) pneumonia patients and compared to patients at the admission to the ICU (controls). Our results show that some AAMs may be more frequently detected in patients who had hospital-acquired pneumonia than in controls, whereas other AAMs are ubiquitously detected. However, ICU patients seem to exhibit increasing immune response to AAMs when the ICU stay is prolonged. Moreover, concomitant antibodies responses against seven different microorganisms (5 Rhizobiales, Balneatrix alpica, and Mimivirus) were observed in the serum of patients that had a prolonged ICU stay.

Conclusions/significance: Our work partially confirms the results of previous studies, which show that ICU patients would be exposed to water amoeba-associated microorganisms, and provides information about the magnitude of AAM infection in ICU patients, especially patients that have a prolonged ICU stay. However, the incidence of this exposure on the development of pneumonia remains to assess.

pone-0058111-g001: The association between a prolonged ICU stay and exposure to amoeba-associated microorganisms.The blue period corresponds to the period where a majority of the hospital-acquired pneumonia episodes (>95%) occurred. The CAP episodes mainly occurred from 12 to 24 hours after admission (green period). d; day.

Mentions:
To study the effects of a prolonged ICU stay on exposure to AAMs, we separately computed mean number of microorganisms against which the patients exhibited an antibody response for admission serum samples (n = 29) and for samples collected every 7 days thereafter (weekly serum samples; n = 56). Data indicate that the number of organisms against which patients (with or without pneumonia) exhibit an immune response (essentially with IgM antibodies) is positively correlated with the length of the patient ICU stay (Fig. 1). Overall, our patients developed an antibody response to an increasing number of AAMs over time, especially from days 7 to 21 following their admission (Fig. 1). These findings highlight the high seroconversion rates exhibited by ICU patients during their stay (Table 4) and confirm that immune response to AAMs increases when the ICU stay is prolonged.

pone-0058111-g001: The association between a prolonged ICU stay and exposure to amoeba-associated microorganisms.The blue period corresponds to the period where a majority of the hospital-acquired pneumonia episodes (>95%) occurred. The CAP episodes mainly occurred from 12 to 24 hours after admission (green period). d; day.

Mentions:
To study the effects of a prolonged ICU stay on exposure to AAMs, we separately computed mean number of microorganisms against which the patients exhibited an antibody response for admission serum samples (n = 29) and for samples collected every 7 days thereafter (weekly serum samples; n = 56). Data indicate that the number of organisms against which patients (with or without pneumonia) exhibit an immune response (essentially with IgM antibodies) is positively correlated with the length of the patient ICU stay (Fig. 1). Overall, our patients developed an antibody response to an increasing number of AAMs over time, especially from days 7 to 21 following their admission (Fig. 1). These findings highlight the high seroconversion rates exhibited by ICU patients during their stay (Table 4) and confirm that immune response to AAMs increases when the ICU stay is prolonged.

Bottom Line:
Amoeba-associated microorganisms (AAMs) are frequently isolated from hospital water networks and are reported to be associated to cases of community and hospital-acquired pneumonia.Our results show that some AAMs may be more frequently detected in patients who had hospital-acquired pneumonia than in controls, whereas other AAMs are ubiquitously detected.Our work partially confirms the results of previous studies, which show that ICU patients would be exposed to water amoeba-associated microorganisms, and provides information about the magnitude of AAM infection in ICU patients, especially patients that have a prolonged ICU stay.

Background: Patients admitted to intensive care units are frequently exposed to pathogenic microorganisms present in their environment. Exposure to these microbes may lead to the development of hospital-acquired infections that complicate the illness and may be fatal. Amoeba-associated microorganisms (AAMs) are frequently isolated from hospital water networks and are reported to be associated to cases of community and hospital-acquired pneumonia.

Methodology/principal findings: We used a multiplexed immunofluorescence assay to test for the presence of antibodies against AAMs in sera of intensive care unit (ICU) pneumonia patients and compared to patients at the admission to the ICU (controls). Our results show that some AAMs may be more frequently detected in patients who had hospital-acquired pneumonia than in controls, whereas other AAMs are ubiquitously detected. However, ICU patients seem to exhibit increasing immune response to AAMs when the ICU stay is prolonged. Moreover, concomitant antibodies responses against seven different microorganisms (5 Rhizobiales, Balneatrix alpica, and Mimivirus) were observed in the serum of patients that had a prolonged ICU stay.

Conclusions/significance: Our work partially confirms the results of previous studies, which show that ICU patients would be exposed to water amoeba-associated microorganisms, and provides information about the magnitude of AAM infection in ICU patients, especially patients that have a prolonged ICU stay. However, the incidence of this exposure on the development of pneumonia remains to assess.